Washing machine with sensor means

ABSTRACT

A washing machine comprises a tank for loading washing fluid and items to be washed and a control adapted to carry out a predetermined washing program. The washing machine comprises a first electrode electrically insulated from the washing fluid and a sensor connected to the first electrode for detecting a value of a sensor formed by the first electrode and by the washing fluid acting as a second electrode, the value being fed to the control in order to control and/or adjust the washing program.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a washing appliance comprising a tankfor loading washing fluid and items to be washed and a control adaptedto carry out a predetermined washing program.

2. Description of the Related Art

Washing appliances, for instance washing machines or dishwashers, carryout a program selected by the user on the basis of the amount and degreeof soil of items. With the term “washing program” we mean hereby theentire program carried out by the appliance or a portion thereof.Usually, in the case of a laundry washing machine, the washing programcomprises also the rinsing and spinning steps. Some washing applianceshave sensors for detecting automatically the load and other parametersin order to self-adjust the washing program.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a washing appliancehaving a detection system able to assess the working condition thereofin a reliable and economical matter, and for assuring a self-adjustmentof the washing process. According to the present invention, theappliance comprises at least a first electrode electrically insulatedfrom the washing fluid and a sensor connected to the control and to thefirst electrode and adapted to detect a value of a sensor formed by thefirst electrode and by the washing fluid acting as a second electrode,the value being fed to the control in order to control and/or adjust thewashing program. The sensor and the control can be parts of a singleelectronic control unit. The value detected by the sensor is indicativeof a capacitance and/or a complex impedance of the two electrodes.

DESCRIPTION OF THE PREFERRED EMBODYMENT

In a preferred embodiment of the invention, the sensor essentiallyconstitutes a capacitor. The first electrode is preferably a metal plateisolated from the washing fluid by a dielectric, for instance theinsulating wall of the tank made of polymeric material. The secondelectrode of the capacitor is formed by the washing fluid (wash fluid inthe tank or receptacle). The electrical connection between the detectorand the washing fluid is made through a metal body, for instance throughthe heating element body. The first electrode is spatially arranged sothat wetting with washing fluid of the respective dielectric can occur.Preferably the first electrode is above the fluid level of the washingfluid as the temporarily applied fluid film can run off there.

In the case of a plastic tub the dielectric can be the tub itself, andthe first electrode surface may then be arranged at various locations onthe exterior of the tub or inserted in various locations into the tubwall respectively. The embodiment in which the first electrode isintegral with the tub wall (for instance through a process ofco-injection during the injection molding of the plastic tub) alsoprovides a variety of functional benefits: simultaneous attachment ofthe electrodes prevents conductive contact of the electrode withpotential impurities on the exterior of the tub (dirt buildup on theexterior of the tub, water condensation on the exterior of the tub, itreduces the distance between the metal or permanent electrode plate andthe electrode sheet formed by the fluid film and subsequently increasesthe sensitivity of the electrode system).

The dielectric and the first (permanent) electrode can be arranged notonly in the tub, but also in the drain tube or in an external chamberthat is wetted by a specially controlled pump. The first electrode canbe composed by several distinct electrodes geometrically arranged in thecase of the plastic tub that electrically isolates and acts as adielectric, or in a plastic tube (in which the washing fluid flows) onthe exterior thereof and/or with electric insulation also within the tubor tube respectively. In the case of an electrically conductive tank,e.g. a stainless steel tank, the capacitive sensor may be realizedcompletely within the tank or completely outside the tank respectively.

The spatial arrangement is always chosen thereby such that throughcontrolled wetting of the dielectric with fluid (e.g. by drum movement,or by a special pump) the result is a ground electrode with a variablesurface. The film, which is the result of controlled wetting, (variableplate capacitor in the area of the permanent electrode) then runs off inthe gravitational field after controlled wetting on account of thespatial arrangement. In addition, wetting can be intentionallyinterrupted, for example, by the pump or the drum movement in order torecord the runoff flow in terms of time. The variation in the signalfrom the capacitive sensor gives information on the detergentconcentration, the degree of rinsing and other important parameterswhich may be used to control the washing program.

Furthermore, wetting by the drum can also occur continuously, e.g. bythe wash fluid entrained by the drum at a certain rotation speed and therunoff of the wash fluid on the receptacle wall, so that an equilibriumcan be reached and a constant wash fluid level is achieved. The heightof this level depends on the properties of the wash fluid. The resultingsignal (capacity) is indicative of the mechanical properties of theboundary layer of the wash fluid on the sensor surface based on therunoff process on the sensor surface, and/or on an arbitrary surface,like fiber surfaces, for example, when washing and rinsing clothes. Itis known that the mechanical properties of the boundary layer influencethe washing process of fibers and/or arbitrary surfaces and the rinseprocess of fibers and/or arbitrary surfaces. Subsequently, it can beused in part to monitor wash and rinse processes and to actively controlby an adjustment process. The progression of such processes can be madevisible through a display in the user field area.

The sensitivity of the signal is set by the size of the sensor surfaceand/or its arrangement. Vertical arrangement of the first sensor ispreferred for the signal during the washing process. A flatterarrangement is better during rinsing, since with increased rinsingaction the fluid and/or film runs off more easily. In order to havealways the best arrangement in different steps of the appliance cycle,different permanent electrode surfaces can thus be compiled into onemultifunctional sensor. According to such embodiment, the firstelectrode can be divided into individual segments of known geometricarrangement. Subsequently, an arbitrary characteristic diagram curve canbe plotted through targeted arrangement of the individual condensercomponents.

If the individual electrode segments are wetted from bottom to top as itmay happen in a tub of an horizontal axis washing machine, for exampleby drum movement, than one obtains a discreet step signal, the traits ofwhich can clearly be assigned to “levels” and/or a wetted sensorsurfaces, as the surfaces and/or the sensor data of the individualcomponents are known. This makes automatic calibration possible withsoftware, which can be repeated as desired when the characteristicsignal is attained. The distribution of the electrodes into segmentsalso allows the electrode segments to be mounted in other places, e.g.to record the fluid column upstream from the discharge pump in order tobe able to control turning the pump on and off in order to prevent airsounds in the pump, for example.

The first electrode surface should be arranged such that the filmrunning off on its dielectric is influenced the least possible bydisturbances. A disturbance can be a film running off from the above,for example. Using a shaped deflector on the inside surface of the tubthis undesired running off is avoided, since the deflector leads thefluid and/or fluid film from above past the relevant sensor surface.Disturbances can also occur due to films from softeners or otheradditives. For the sake of prevention, the sensor surface is preferablyrinsed with freshwater. This special rinsing can be integrated into theprogram sequence such that after the softening cycle and/or afterintroduction of any additives the relevant surface of the sensor can berinsed with the aid of a special chamber that can be filled with freshwater and subsequently purifies the film caused by the softener and/oradditives. The whole sensor rinsing process can be repeated for controlsurveys.

The same device is used to differentiate suds from the film presentduring the wash process. Suds keep flowing again independently afterrinsing and therefore usually cause the same signal. A wash-active filmcaused by the wash fluid is removed and/or weakened during rinsing. Thesignal returns only after active wetting, i.e. as described in theexample above by rotation of the receptacle. The program control canevaluate this information and if necessary already optimize the programwith special suds routines during the wash process.

It is preferred to integrate a reference capacity in the sensor whichenables extensive elimination of temperature effects (temperaturecoefficient of different substances), life span drift by changing thesubstance and influences of various detergents, soil and water.

A sensor used in a washing machine according to the invention is simpleand robust (no moving parts, conductive and isolating surfaces withintegrated electronics) and it produces a signal already during washingthat correlates with many parameters important for the wash and/or rinseand spin cycle:

-   -   Under and/or over-proportioning of wash substances    -   Changes (consumption) of wash activity of the fluid    -   Concentration balance when rinsing    -   Rinse effect, rinse result    -   Occurrence of foam/suds during the wash and rinse process    -   End of rinse    -   Reference level when water flows in    -   Spray water when spinning

By already having these parameters during operation, further washingprogram optimization is made possible together with already knownparameters, in particular:

-   -   Automatic proportioning and/or re-proportioning of detergents    -   Ancillary automatic wash time adjustment of wash time for        extreme soiling    -   Partially regulated and/or automatic rinse process (time, water        amount, quantity, mechanical system)    -   Improved online display of the wash, rinse and spin programs    -   Suds monitoring with active program change    -   Indication: Under/over-proportioned, suds    -   Controlled centrifuge turns    -   Pump motor control

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in the following by way of examplewith reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a partially sectioned washing machineaccording to the invention, in which the outside of the tub is shown;

FIG. 2 is a perspective view of a section taken along line II-II of FIG.1, in which the inside of the tub is shown;

FIG. 3 is a schematic circuit diagram of a washing machine of FIGS. 1and 2.

DETAILED DESCRIPTION

With reference to the drawings, a washing machine comprises a plastictub 10 having an outside cylindrical surface 10 a. In the plastic tub 10there is provided a rotating drum (whose only the rear portion 20 isshown in FIG. 2) driven by a motor 11. The tub 10 is loaded with freshwater through valves 8 and through a detergent bin 9. On the outsidesurface 10 a of the tub 10 there are placed three measuring electrodes4-6 and a reference electrode 7. These electrodes are connected to anelectronic unit 2, such unit being linked to a control process unit 22of the washing machine (FIG. 3). The electronic unit is also linked to aheating element 12 placed in the tub, which is used also as electricalconductor in the washing fluid.

On the inside surface of the tub, indicated with the reference 10 b, adeflector 3 is placed which acts as a fluid film tear-off device. Thefunction of the deflector 3, which has an axis inclined with referenceto the axis of the tub, is to channel the fluid coming down from theupper portion surface of the tub away from the zone where electrodes 4,5and 6 are placed, in order to avoid the already mentioned problem ofdisturbance.

For avoiding the other disturbance problem due to the use of softenersor additives, the tub 10 presents a fresh water inlet nozzle 8 a (FIG.2) fed by an external chamber 1 (FIG. 1). The nozzle 8 a faces thesensor surface and continuously supplies a defined amount of water. Whenrinsing the sensor, it is crucial that the entire surface is rinsed.This is achieved in that more freshwater flows into the chamber 1 thanflows off below via the nozzle 8 a. Thus the chamber 1 fills withfreshwater. Subsequently, increasing static pressure results and thewater running off thus successively reaches the entire surface of thesensor. The freshwater is shut off when the chamber is full. The waterflowing off again has increasingly less pressure and the streamgradually diminishes. The volume of the chamber 1 is designed such thatin most cases it cleanses the sensor.

Even if in the above description reference was made to a measurement ofcapacitance, nevertheless expanded assessment of the capacitive sensormay include provisions for measuring its complex impedance, allowingfurther interpretations of the measurement signal. This allows anenhanced signal evaluation including vectorial evaluation of theimpedance of the entire system subject to the frequency. It is to beexpected that thin layers, films, fluid medium, powder and suds can bedifferentiated therewith.

According to the above features, a washing appliance according to theinvention may assess many parameters of the wash program, as amount ofdetergent in wash and/or rinse water, soil amount in the wash water,wash activity of the wash water, rinse efficiency, suds and foamsoccurrence, and level of the wash water, these parameters being used forcontrolling and optimizing the wash program. Moreover, the signal formthe sensor can be used to monitor of the discharge pump too.

1. A washing appliance, comprising: a tank for loading washing fluid anditems to be washed; and a control adapted to carry out a predeterminedwashing program; wherein it comprises at least a first electrodeelectrically insulated from the washing fluid and a sensor connected tothe control and to the first electrode and adapted to detect a value ofa sensor formed by the first electrode and by the washing fluid actingas a second electrode, the value being fed to the control in order tocontrol and/or adjust the washing program.
 2. A washing applianceaccording to claim 1, wherein the value detected by the sensor isindicative of capacitance and/or complex impedance of the electrodes. 3.A washing appliance according to claim 1, wherein the first electrode isplaced on the outside surface of the tank.
 4. A washing applianceaccording to claim 2, wherein the tank is a cylinder having asubstantially horizontal axis, wherein the first electrode is placed onthe cylindrical surface of the tank in a intermediate position betweenthe bottom and the upper portion of the tank.
 5. A washing applianceaccording to claim 3, wherein the first electrode comprises a pluralityof electrodes placed in different positions on the tank.
 6. A washingappliance according to claim 1, wherein the electrical connectionbetween the sensor and the washing fluid is made through a heatingelement or through an additional electrode placed in the tank.
 7. Awashing appliance according to claim 3, wherein on the internalcylindrical surface of the tank a deflector is placed for protecting azone corresponding to the first electrode from the washing fluid flowingfrom the upper portion of the tank.
 8. A washing appliance according toclaim 1, further comprising: a reference electrode connected to thesensor and adapted to correct the value indicative of capacitance and/orcomplex impedance from external factors.
 9. A washing applianceaccording to claim 1, further comprising: a nozzle fed by a chamberplaced outside the tank for cleaning an inside zone of the tankcorresponding to the first electrode.
 10. A washing appliance accordingto claim 1, wherein the tank is made of polymeric material, wherein thefirst electrode is co-injected in the wall of the tank.
 11. A washingappliance according to claim 1, wherein the information provided by thesensor is used for assessing one or more parameters comprised in thegroup consisting of amount of detergent in wash and/or rinse water, soilamount in the wash water, wash activity of the wash water, rinseefficiency, suds and foams occurrence, and level of the wash water,these parameters being used for controlling and optimizing the washprogram.
 12. A washing appliance according to claim 12, wherein theinformation provided by the sensor is used to control the discharge pumpmotor.